What is CVE-2026-40864?

CVE-2026-40864 is a medium-severity vulnerability in Jupyter Jupyterhub, classified under Cross-Site Request Forgery (CSRF). CVSS score: 5.4/10. Published 2026-05-22.

How severe is CVE-2026-40864?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Is CVE-2026-40864 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

CSRF in Jupyter Jupyterhub

CVE-2026-40864

JupyterHub is software that allows users to create a multi-user server for Jupyter notebooks. In versions 4.1.0 through 5.4.4, XSRF protection (updated in 4.1.0) inappropriately treated requests with Sec-Fetch-Mode: no-cors as same-origin…

Vulnerability class: CSRF (Cross-Site Request Forgery)

EPSS: 0.002 (5.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L.

Affected products

Jupyter Jupyterhub
Jupyterhub — versions >= 4.1.0, < 5.4.5

Weakness classification (CWE)

CWE-352 — Cross-Site Request Forgery (CSRF)

Public proof-of-concept exploits

romain-deperne/CVE-2026-40864

References

security-advisories@github.com (x_refsource_CONFIRM, Mitigation, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)

Frequently asked questions

What is CVE-2026-40864?: CVE-2026-40864 is a medium-severity vulnerability in Jupyter Jupyterhub, classified under Cross-Site Request Forgery (CSRF). CVSS score: 5.4/10. Published 2026-05-22.
How severe is CVE-2026-40864?: Medium severity. CVSS v3 base score is 5.4 out of 10.
Is CVE-2026-40864 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.